The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Intake valves control the entry of an air/fuel mixture into cylinders of an internal combustion engine (ICE). Exhaust valves control the exit of gases from the cylinders of an internal combustion engine. Camshaft lobes (or “cam lobes”) on a camshaft push against the valves to open the valves as the camshaft rotates. Springs on the valves return the valves to a closed position. The timing, duration, and degree of the opening, or “valve lift,” of the valves can impact performance.
Variable valve actuation (VVA) technology improves fuel economy, engine efficiency, and/or performance by modifying the valve event lift, timing, and duration as a function of engine operating conditions. Two-step VVA systems enable two discrete valve events on the intake and/or exhaust valves. The engine control module (ECM) selects the optimal valve event profile that is best utilized for each engine operating condition.
An issue in the development and application of VVA system is the response time variability of the control system and hardware. A limited amount of time is available for switching a Switching Roller Finger Follower (SRFF) between engaging and disengaging. If the control valve causes a fluid pressure change in a lifter fluid gallery to occur too soon relative to a valve lift curve, a SRFF arm lock pin may only partially engage and then disengage after the valve has started lifting. This unscheduled disengagement may cause the engine valve to drop from the high-lift valve event to the low-lift valve event, or on to the valve seat. After a number of such events, the SRFF arm or the valve may show signs of accelerated wear or damage.